Phosphate bonded magnesite-chrome brick

ABSTRACT

Magnesite-chrome ore brick having a sodium phosphate binder and extremely high tensile strength as a result of the formation, in service or in burning in a kiln of a calcium sodium silicophosphate bond.

United States Patent Ben Davies; 1

George F. Carini, both of Pittsburgh, Pa. 734,042

June 3, 1968 Oct. 26, 1971 Dresser Industries, Inc.

Dallas, Tex.

[72] Inventors [21] Appl. No. [22] Filed [45] Patented [73] Assignee [54] PHOSPHATE BONDED MAGNESlTE-CHROME BRICK 7 Claims, 2 Drawing Figs.

US Cl 106/59 C041: 35/42 50 FieldofSearch 106/58,59

[56] References Cited UNITED STATES PATENTS 3,522,063 7/1970 Treffner et al 106/59 3,304,187 2/1967 Limes et al. 106/59 3,392,037 7/1968 Neely et a1 106/58 Primary Examiner-James E. Poer Attorneys-Robert W. Mayer, Raymond T. Majesko and David C. Hanson ABSTRACT: Magnesite-chrome ore brick having a sodium phosphate binder and extremely high tensile strength as a result of the formation, in service or in burning in a kiln of a calcium sodium silicophosphate bond.

PHOSPHATE BONDED MAGNESITE-CHROME BRICK percent, by weight. Optimum results are obtained when the silica content is less than 0.75 percent, by weight. It is prefera- BACKGROUND Magnesite-chrome ore brick are manufactured substantially from dead burned magnesia, which in the refractories art is termed magnesite, and refractory grade chrome ore. In these brick, the magnesite is the major ingredient and the chrome ore the minor ingredient. Chemically bonded brick are those which are not treated by a firing or burning process prior to use. Ceramically bonded brick are burned at temperatures generally in excess of 2500 F.

This patent is closely related to U.S. Pat. No. 3,479,994, issued Nov. 18, 1969 by the same inventors. That application discloses chemically bonded magnesite brick having a calcium sodium silicophosphate bond. This invention is directed to ceramically or chemically bonded magnesite-chrome ore brick. Brick made according to the teachings of this invention may be used, among other places, in the walls of steelmaking open hearth furnaces, in induction furnaces used for melting ferrous and nonferrous metals, and in glass tank regenerator walls and checker settings.

Accordingly, it is an object of this invention to provide magnesite-chrome ore brick with improved tensile strength (as measured by transverse loading or modulus of rupture.) It is another object of this invention to provide a magnesitechrome ore brick with a sodium phosphate binder that has av modulus of rupture at 2700 F in excess of 500 p.s.i.

BRIEF DESCRIPTION This invention is predicated upon the discovery that sodium phosphate glasses, when reacted at intermediate temperatures with certain lime and silica-yielding materials, can impart high temperature strength to magnesite chrome ore brick when the CaO:SiO :P weight ratio of the brick is sufficiently close to 55:12:33. Brick made according to this invention are formed, for example, from a batch consisting essentially of size-graded dead burned magnesite grain and chrome ore and a sodium phosphate glass binder such that the brick typically have a CaO:SiO,+CQ2O weight ratio between 111.06 and 1:1.50 and a CaOzSiO weight ratio between 2.65:1 and 12.5:1. The P O :CaO+SiO ratio must be greater than 0.28:1. Stated another way, the CaO:SiO,: P 0, ratio typically should fall within area A-B-C-D-E on FIG. I. Preferably, the CaO:SiO,:P,

O ratio should fall within area F-G-H-I on FIG. I. The B,O content of brick according to this invention should be less than about 0.08%, by weight. The sodium phosphate binder should yield at least 0.75% P The total CaO+SiO,+P O in.

the brick should preferably be less than Preferably, the dead burned magnesite should be at least 90% MgO. It is preferable that the silica content of the brick be less than 1.5

ble that the magnesite to chrome ore weight ratio be between about :10 and 60:40 and that the chrome ore be sized to pass 14 mesh and rest on mesh. Burned brick according to the teachings of this invention can be made from unburned shapes formed from batches described above and burned at temperatures in excess of 2800 F.

In order that the brick according to this invention have appropriate CaO:SiO :P O ratios, it is necessary that they be prepared from batches in which the magnesite is prepared having a suitable CaOzSiO; ratio or in which calcium-yielding materials are added to the batch such as calcium carbonate, calcium ferrite, calcium aluminate, calcium chromite, or mixtures thereof. According to another aspect of this invention, burned magnesite-chrome ore brick are prepared having an appropriate CaOzSiO ratio and are thereafter impregnated with sufficient soluble phosphate to provide the brick with a CaO:SiO :P, weight ratio, according to the teachings of this invention.

Burned brick according to the teachings of this invention display an unusual microstructure. It is characterized by periclase grains bonded partially by calcium sodium silicophosphate phase and partially by a complex spine] phase BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a ternary diagram which shows the CaO:SiO,:P,O,, ratios suitable in brick according to the teachings of this invention.

FIG. 2 contains X-ray diffraction patterns of examples hereinafter discussed.

DETAILED DESCRIPTION Further features and other objects and advantages of this invention will become clear to those skilled in the art by a careful study of the following detailed description. In the detailed description, all sizings are reported by Tyler screen series; all percentages and parts are by weight; chemical analyses were obtained by spectrographic analysis with control by wet chemical analysis, and are reported as oxides in accordance with the present practice of the refractories industry.

The detailed discussion is made with reference to FIG. 1 which is a ternary diagram on which the relative proportions of CaO:SiO,:P,O of the brick according to the teachings of this invention are outlined. Proportions are calculated from the'chemical analysis without reference to MgO, or other oxides, the major components of the refractory which, of course, have no influence on the proportion of the CaO, SiO,, and P 0 This invention is based on the discovery that certain calcium sodium silicophosphates provide a refractory bond for TABLE I Example Batch (parts by weight):

Dead burned magnesite A Philippine chrome ore Calcium carbonate Sodium metaphosphate... Portland cement Type III Calcium ferrite 2. 25 2. 25 Calcium aluminate cement 4. 6 Burn, F 3,150 Bulk density, p.c.t 200 199 194 187 190 192 188 I94 194 Apparent porosity, percent after heating to 2,000 F) 17. 2 16. 7 16. 4 16. 9 17. 8 17. 8 16. 0 15.4 15. 4 Modulus oi rupture, p.s.i.:

At roo'n temperature 1, 2 0 1, 400 2, 610 1, 570 2, 570 1, 350 1,470 1,430 1,770 At 2,700 F 1, 010 1, 1, 660 1, 260 1, 300 670 1, 450 1, 1, 510 Rgiaive proportion 01 CaO, S10: and

z 5: CaO 59. 4 56. 3 53. 0 56. 5 55. 9 59. 3 54. 1 54. 5 51. 6 S102- 1.3. 5 15. 1 10. 9 14. 5 10.9 17. 6 13. 2 16. 1 14. 9 P205 27. 1 28. 6 36. 1 29. 0 33. 2 23. 1 32. 7 29. 3 id- 4 Chemical analysis (percentage):

Silica (S102) 0.64 0. 68 0.75 0.65 0.81 0.95 0.65 0.71 i). 55 Alumina (AIzO 6. 2 4. 7 3. 3 1. 8 6. 7 8. 5 6. 4 3. 4 3. 4 Iron Oxide (F920 11. 1 8. 2 5. 8 3. 1 3. 1 8. 5 5. 4 7. 1 7. 2 17. 6 13. 0 9. 3 4. 8 6. 5 13. 1 8. 5 9. 1 7. 9 2. 81 2. 54 3. 66 2. 54 4.15 3. 20 2. 70 2. 40 1.90 l1 By diiierencc Phosphorous oxide (PO 1. 28 1 29 2. 49 1. 3O 2. 46 1. 25 1. 63 1. 29 1. 39 Boron oxide (BzO 0. 0 0 0 0 0 0. 0 0 0. 0 0 0. 0 0 0. 0'0 0. 060 0. 0 0 0. 0' 0 Soda (N8 0) 0.60 0.60 1. 16 0.60 1. 14 0.58 0.75 0.60 0.64

Less than amount reported.

' magnesite-chrome ore brick. Briefly, we have found that those brick either burned or unburned which have a CaO:SiO :l=' O weight ratio sufficiently near 55:12:33 have unexpectedly high tensile strength. (The oxide ratios referred to in this specification are by weight.) This discovery is indeed surprising as in the past it has generally been considered that lime should be maintained as low as possible in magnesite-chrome ore brick.

Examples A through I, the batches in parts by weight and properties of which are shown in table I, are according to the teachings of this invention. They were prepared from sizegraded batches of dead burned magnesite, chrome ore, and lime-yielding materials and a sodium metaphosphate glass binder. The chemical analyses of the chrome ores and magnesites are given in table VIII. The batches were tempered with water and pressed into brick at about 1200 p.si. The brick were dried to about 250 F. for about 10 hours and thereafter tested for bulk density, apparent porosity, modulus of rupture at room temperature and at 2700 F. The chemical analyses were also determined. Example I was given the additional treatment step of being burned at 3150 F. prior to testing.

Table I establishes that a brick made according to the teachings of this invention has strength, as measured by modulus of rupture at2700, in excess of 500 p.s.i. and often in excess of 1000 p.s.i. Table 1 also establishes that various magnesitezchrome ore ratios can be used in the practice of this invention. Also, the table establishes that different types of chrome ore can be used, such as Transvaal chrome ore or Phillippine chrome ore. It should be mentioned, however, that chrome ore satisfactory for use in this invention must have a low sicica content preferably below 1.5 percent but satisfactorily below 3 percent. Table I further establishes that various lime-yielding materials can be used in order to supply sufficient lime to the brick such that the brick will have a satisfactory CaO:SiO,:P,O ratio.

To obtain a better understanding of our invention, X-ray diffraction studies of Examples A, B, C, and D were made immediately after the sample brick were dried at 500 F. and after they had been tested for modulus of rupture at 2700 F. The diffraction patterns are given in FIG. 2. Immediately after drying, the brick contained calcite and sodium phosphate (amorphous to X-rays) and phases typically associated with dead burned magnesite (FIG. 2 a, b, c, d). After heating to 2700 F, however the phase assemblage is entirely different. A calcium sodium silicophosphate phase had been formed FIG. 2 a, b, b, c',d'). Standard X-ray powder diffraction procedures were followed.

To obtain a still better understanding of our invention, the distribution of selected elements was determined from X-ray (Ka) images of various areas of polished surfaces of examples H and I using an electron probe X-ray microanalyzer. These examples were prepared in the same manner except that example H was heated to 2700 F. in the modulus of rupture test and example I was fired at 3150 F.

The electron microprobe X-ray images established that example I-I, which is an unburned brick but tested after heating to 2700 F, comprises magnesite and chrome ore grains bonded together by a calcium sodium siliconphosphate phase. The X-ray images showed that example I, which is a brick burned at 3 150 F., comprises periclase grains containing complex spinel inclusions bonded by a complex spinel phase and a calcium sodium silicophosphate phase.

The calcium sodium silicophosphate solid solution is developed in a solid state reaction between sodium phosphate and various lime and silica-yielding materials at relatively low temperatures (below 2300 F.) aided, apparently, by the reaction-accelerating effect of the sodium cation. The refractoriness of the system is not affected detrimentally by the limited presence of sodium. Sodium enters the calcium silicophosphate structure filling vacant calcium positions in the lattice which are unoccupied because of the difference in valence between SiO and P0,, groups. In our experience the soda can be present in an amount less than about 0.5 times the P weight percent. Substances, particularly solid solutions,

and thereafter with unoccupied cation positions are not unusual. In effect, the sodium ions are isolated and not available for reaction with other components to form low melting compounds. The structure of the calcium sodium silicophosphate solid solution is analogous to the high temperature form of the calcium silicophosphate solid solution series suggesting that sodium effectively stabilizes the calcium silicophosphate structure in its high temperature form. Strength variations at elevated temperatures, attributable to structural inversions, are consequently eliminated.

The examples whose properties are recorded in table I were prepared according to one technique in which lime-yielding materials were added to the batch with the magnesite and chrome ore. Another technique is to combine chrome ore with a magnesite having an appropriate limezsilica ratio. It is very difficult to incorporate magnesites having limezsilica rations in excess of about 3:1 in brickmaking batches because of the tendency to have free lime in the magnesite that will hydrate. Therefore, it is usually necessary that magnesites having high lime: silica ratios also contain an appropriate amount of iron oxide, chromic oxide, or alumina to react with and tie up any free lime that might be present in the magnesite. Examples .I and K were prepared from a magnesite having a lime to silica ratio of about 4:1 and sufficient iron oxide to make the magnesite usable in brickmaking batches. The chemical analysis of this magnesite is given in table VIII. The batch comprised parts magnesite and 20 parts Transvaal chrome ore and 2.2 parts sodium metaphosphate glass binder. The chrome ore was sized to all pass 14 mesh and rest on 65 mesh. The magnesite was sized so that approximately 30 parts was 4+l0 mesh, 15 parts l0+28 mesh, and 35 parts was ball mill fines which were substantially all 65 mesh. The batches were tempered with water and pressed into shapes at about 12000 p.s.i. They were thereafter dried. Example K was thereafter burned at 3150 F. The batches and the properties of exemplary mixes .I and K are given in table II.

It should be noted that the chemical analyses of examples .1 and K differ. This is due to a minor loss of lime and silica during the burning at 3150 F. Other examples throughout this specification may have chemical analyses that differ from what might be expected considering the chemical analyses of the starting materials. This is simply because the chemical analyses of the starting materials vary somewhat. For this reason, they are described in table VIII as typlcal.

TABLE 11 Example; J K

Butch (parts by weight):

Dead burned magnesite B 80 Transvaal chrome oro 20 Sodium metaphosph 2. 2 Burn, F 3,160 Bulk density, p.c.l'. 195 Apparent porosity, percent (after heating to 2 00F- 12.1 14.1) Modulus of rupture, p.s.i.:

At room temperature 1, 310 1, 530 At 2,700 F 1,380 1,030 Relative proportion of 0:10, S102, and P:

CaO 56. 6 51. 2 15. 2 14. 6 28. 3 34. 1

0.75 0. G0 3. 50 3. 50 7. 5 7. 5 8. 1 8. 0 2. 80 2. 10 Magnesia (MgO) y difference Phosphorous oxide (P20 1. 43 l. 50 Boron oxide (B203? 0. 080 0. 030 Soda (NazO) 0. 86 0.70

*Less than amount reported.

Table II establishes that brick having outstanding high temchrome ore, sodium phosphate and a magnesite with an appropriate CaOzSiO ratio.

Another method of making magnesite-chrome ore brick according to this invention consists of preparing a burned magnesite-chrome ore brick having an appropriate CaOzSiO ratio impregnating the brick with sufiicient phosphate binder to adjust the CaO:SiO :P O ratio.

Examples L to P were prepared to show the effect of varying the CaO:SiO +P O ratio in magnesite-chrome ore brick. The batches for these examples are given in table 111.

amples were added increasing amounts of boric acid. The batches from which these examples were prepared and their properties are given in table V.

TABLE 111 Example L M N O P Batch (parts by weight):

Dead burned magnesite A 80 80 80 80 80 Transvaal chrome re .20 20 20 20 20 Calcium earb0nate 2.0 Calcium ferrite 3.0 4.94 Calcium aluminate cement 4. 3 4.6 Sodium metaphosphate-. 1. 7 2. 28 3. 0 2. 6 3.0 Bulk density, p.c.f 195 189 196 188 193 Apparent porosity, percent (after heating to 2,000 F.) 15. 7 17. 1 15. 1 16. O 17. 0 Modulus of rupture, p.s.'

At room temperature 950 1, 480 1,700 1, 470 1,970 At 2,700 F 280 1, 060 1, 260 1, 450 390 Rglaive proportion of CaO, S10 and C210 60. 6 57.1 55.8 54. 1 52. 0 $10 13.7 13.1 12.9 13.2 13.3 P 05 25.6 29.8 31.3 23.7 34.7 CaO;S1O +P O5 1. 55: 1 1.33:1 1. 28 :1 1.18: 1 1.08: 1 Chemical analysis (percentage):

'lica (S102 0.60 0.02 0.75 0.66 0.75 Alumina (A1203) 3. 5 6.1 34. 6.4 3.1 Iron oxide (Fe O 7. 9 6.0 8. 2 5.4 5.4 Chromie oxide 9. 5 9. 4 0.2 8.5 8. 5 Lime (C210) 2. 65 2. 70 3. 24 2. 70 2. 92 Magnesia (MgO) By diflerence Phosphorous oxide (1 205)... 1.12 1.41 1. 82 1. 63 1. Boron oxide (13 0 0.030 0.030 0.030 0.0 0. 030 Soda (N320) 0.51 0.64 0. 0.75 0.90

Less than amount reported.

Table [II establishes that the proper CaO:SiO +P O ratio is an essential feature of this invention. Example L contained too much CaO in relation to SiO and P 0 present. Example P, on the other hand, has too little lime. Examples M, N, and 0 have excellent transverse strengths in excess of 1,000 p.s.i. at 2,700 F.

Examples Q through V were prepared in the same manner as examples A through H. These examples all had about the same CaO:SiO +P O ratio but differed in their CaOzSiO ratios. THe batches from which examples 0 through V were prepared and the properties of these examples are given in table IV.

Table V establishes that the boron oxide content of brick made according to the teachings of this invention should be less than about 0.08.

Table VI establishes that best results were obtained when the chrome ore is all passed 14 held on ISO mesh. However, even TABLE IV Example Q R S T U Batch (parts by weight):

Dead burned magneslte A 80 80 80 Transvaal chrome ore 20 20 20 Calcium carbonate Calcium ferrite 2.03 2. 25 Calcium aluminate cement Sodiun metaphosphate 1. 14 2. 0 2. 0 Bulk density, p.c.f 194 103 194 Apparent porosity, percent (after heating to 2,000 F.) 15.8 16. 7 15.4 Modulus of rupture, p.s.i.:

At room temperature 000 1, 220 1, 4' 0 At 2,700 F 440 1, 060 1, 190 Ri laive proportion of C110, 5102, and

C210 55. 6 64. 6 54. 5 SlO2 20. 6 17. 4 16.1 P20 23. 9 8. 0 .29. 3 CaO:SiO2+P2O5 1. 25: 1 1. 20:1 1. 20:1 1. 21: 1 C801 02. 2.7:1 3.121 3.4:1 Chemical analysis (percentage):

Silica (810;) 0. 6') 0.79 0. 71 3. G 3. 4 3. 4 6. 0 6. 6 7. 1 10. 0 8. 8 9. 1 1. 70 2.48 2. Magnesia (MgO) By difierencc Phosphorous oxide (P 0. 73 1. 27 1. 20 1. Boron mide (13203)1 0. 030 0. 0 0 0. 0 0 0. 0'0 Soda (N820) 0. 33 0.59 0.

with the inclusion of ball mill fine chrome ore in the batch, outstanding high temperature strengths are achieved.

By way of comparison, a typical chemically bonded magnesite-chrome ore brick having a lignosulfonate binder was prepared and tested for modulus of rupture at 2700 F. Example EE was prepared in the same way as example C, except that the former has a conventional lignosulfonate binder and the latter a sodium phosphate binder. Example C is over 30 times stronger at 2700 F. than example EE. THe test batch and data for example EE are given in table Vll.

TABLE v Example W X Y Z AA Batch (parts by weight)" Dead burned magneslte A 80 80 80 80 80 Transvaal chrome ore 20 20 20 20 20 Calcium ierrite 2.62 2.62 2.62 2.62 2.62 Sodium metaphosphate. 2. 2.0 2.0 2. 0 2.0 Boric acid 0 0. 08 0. 16 0. 24 0. 32 Bulk density, p.c.f 192 192 192 192 192 Apparent porosity, percent (after heating to 2,000 F.) 16. 7 17. 2 17. 4 17. 2 17. 0 Modulus of rupture, p.s.i.:

At room temperature At 2,700 F 1,120 1,060 450 380 280 Relagive proportion of CaO, SiO and 2 56. 0 55.8 56. 4 55. 7 56. 0 15. 5 16.3 16. 0 16. 2 15.7 28. 5 27. o 27. 7 28.1 28. 2 Chemical ana ysis (percentage):

Silica (S102) 0. 72 0. 76 0. 75 0. 76 0. 73 Alumina (A1203)... 3. 4 3. 5 3. 5 3. 4 3. 3 Iron oxide (F6203 7.1 7. 7 7. 3 7.4 7.2 Chromic Oxide (Cr Oa) 0.1 9. 0.6 9.4 0. 1 Lime (Ca 2. 61 2.6 2.65 2. 62 2.60 Magnesia (Mg0) By difference Phosphorous oxide 1. 33 1. 30 1. 30 1. 32 1. 31 Boron oxide (BO;) 0.020 0.065 0.110 0.155 0.200 Soda (Na O 0. 61 0. 60 0. 60 0. 0. 60

TABLE V1 7 RAW MATERIALS AND TEST PROCEDURES Example BB CC DD By sodium phosphate binders we mean sodium phosphates Batch (parts by weight): which are molecularly dehydrated and polymerized. The have gfgg ggggg gggaf A 80 80 80 a soda to phosphorous ratio generally ranging from 1.111 to Pass 14 1 191 6 on 150 20 16 1: 1.821. These glasses are highly soluble, but retain their Ball mi e fines 0 4 C 310mm carbonate L 45 L 45 L 45 molecular structure well in solutions. Commerc al Sodium metaphosphate 2.0 2.0 2.0 metaphosphate glasses (Na,O:P O ratio 15 1:1) includes figg i g gighg fig'i' 'j 192 192 191 Glass H and Glass A" proprietary products of FMC Cori 5070111 tlemperature 1.250 2 160 Lgg poration, and Calgon a proprietary product of the Calgon 00 00 00 u n 21? fiiiiii iafi'if$5172.85; iifliii' mfiiifiilfsfiiil'fi Q hos hate lass which has an Na 0:? 0 ratio of 1.5:]. The s10..- 16.1 15.8 16.1 P P 2 2 9 0 21.9 21.0 28.0 typical chemical analyses of the magnesite and chrome ores Chemical analysis (percentag i l ggfay u n 5 55 i 5 used in exemplary mixes IS given In the following table.

umine 2 s .3 Iron oxide (FezOR) 5. 8 5. 9 5. 7 TABLE VI" Chromic oxide (C1203). 9. 3 9. 2 9. 2 Lime (CaO) 2. 61 2. 0 2.60 Transvaal Philippine Magnesia (MgO) By difference 40 Magncsflc Chrome Chrome Phosphorous oxide (P205) 1. 30 1. 29 1. 30 A B Qre Boron oxide (B2O3) 0.03 0.03 0.03 Soda (N820) 0. 60 0. 50 0. 60

. Less than amount reported. 0] 034 H" 18 Further by way of comparison, two exemplary phosphate Alumina bonded magncsite-chrome ore brick were prepared by simply adding a sodium phosphate glass binder to typical dead 22 3' 02 L5 2 I burned magnesite and typical chrome ore without attempting Chroma oxide to control the CaO:SiO :P O ratio, for example, by adding (01 0,) 3416 lime-yielding materials. These brick had adequate inter- 50 2-523 2 4 3 as 0 2 o 4 mediate temperature strengths (modulus of rupture at 2300 Magncsia F.) but were weak at 2700 F. which is much nearer the (M50) by difference I05 17.: operating temperature of most furnaces in which magnesiteoxide 002 o 03 l d chrome ore brick are used. The data for examples FF and GO are given in table Vll. This invention is an improvement over A l f h brick of this type as it provides brick with excellent strength at f '9' mg or t e exemplary batches would be as 2 00 o ows.

TABLE VII Pass 4 held on 10 mesh 30% Example EE FF GG Pass 10 held on 28 mesh 30 Batch (parts by weight): Pass 28 held on mesh 10 Dead burned magneslte A 8O 80 P855 65 mesh 30 grgnsvaal ehroglne olrei; 20 12g 0 ium metap osp a e 0 0. Lignogunonate liquor 5 Bulk densities of the samples were determined by ASTM iiulk derslliy, p .tc.f 1 9 8 1 92 292 method cl34-41, Manual of ASTM Standards on Refractory Dpamll N351 y D M t 1 9th 1963 S 5 et se M d l f Modulus of rupture, p.s.1.: a ena e l i P o u 0 At room temperature 1690 4 0 65 rupture at room temperature was determined by ASTM i2 3:388: I; "5 ;?8 138 method Cl33-55, pages et seq. of the same manual; Ri laiye proportion of (3210, S102, and modulus of rupture at 2700 F. was determined similarly to the 2 6&0 4&1 modulus of rupture at room temperature, except the test was 23. 3 18.0 70 performed in an electrically heated furnace. 7 9 Having thus described the invention in detail, and with suffi- 0.63 0.60 cient particularity as to enable those skilled in the art to pracg'g tice it, what is desired to have protected by Letters Patent is 10. 6 9.3 set forth in the following claims. a0 1' 60 We claim: Magnesia (GaO) By difference 75 Phosphorous h' i; b; (137 v 1 13 1. A method of making magneslte-chrome ore brick com- Boi-on oixde (B20;) 0.0 0. 03 0.03 prising the steps of: Soda (NazO) 0 0.16 0.52

Less than amount reported.

1. preparing a batch consisting essentially of dead burned magnesite and chrome ore in a weight ratio between 90:10 and 60:40, said batch analyzing less than 0.08 percent B 2. tempering the batch with a suitable tempering fluid and binder,

3. forming the tempered batch into shapes,

4. burning the shapes at temperatures in excess of 2800" F.,

and

5. impregnating the burned shapes with sufficient sodium phosphate solution to provide a CaO:SiO :P O weight ratio in the shapes within the area A-B-CD-E in FIG. 1.

2. A method according to claim 1 in which the weight ratio of CaO to SiO +P O is between 1:1.06 to 1.50:1 and the weight ratio of CaO to SiO is between 2.65 and 12.5:1 and the P O :CaO+SiO ratio is greater than 0.28: 1.

3. A method according to claim 1 in which the CaO:SiO :P 0,, ratio falls within the area F-G-J -1 on FIG. 1.

4. A method to claim 1 in which the dead burned magnesite is at least percent MgO.

5. A method to claim 1 in which the SiO is less than 1.5 percent, by weight.

6. A method according to claim 1 in which the SiO is less than 0.75 percent, by weight.

7. A method according to claim 1 in which the chrome ore is sized to pass 14 mesh and rest on mesh.

zg g UNlTED STATES PATENT OFFECE CERTIFICATE 0F CORRECTION Patent N 3, 15.??? bated oothpr 96 1 5 Inventor s I Ben Davies and George F. Carini It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

' Claim 3, lirie 2, change "J" to H.-.

Claim line 1, before "to," insert -according--.

Claim 5, line 1, before "to" insert according-- Signed and sealed this 12th day of March 1974.

SEAL) t'test.

DWARD M.FLETCHER,JR. I c. MARSHALL DANN ttestingOfficer Commissioner of Patents 

2. tempering the batch with a suitable tempering fluid and binder,
 2. A method according to claim 1 in which the weight ratio of CaO to SiO2+P2O5 is between 1:1.06 to 1.50:1 and the weight ratio of CaO to SiO2 is between 2.65 and 12.5:1 and the P2O5:CaO+SiO2 ratio is greater than 0.28:1.
 3. A method according to claim 1 in which the CaO:SiO2:P2O5 ratio falls within the area F-G-H-I on FIG.
 1. 3. forming the tempered batch into shapes,
 4. burning the shapes at temperatures in excess of 2800* F., and
 4. A method according to claim 1 in which the dead burned magnesite is at least 90 percent MgO.
 5. A method according to claim 1 in which the SiO2 is less than 1.5 percent, by weight.
 5. impregnating the burned shapes with sufficient sodium phosphate solution to provide a CaO:SiO2:P2O5 weight ratio in the shapes within the area A-B-C-D-E in FIG.
 1. 6. A method according to claim 1 in which the SiO2 is less than 0.75 percent, by weight.
 7. A method according to claim 1 in which the chrome ore is sized to pass 14 mesh and rest on 150 mesh. 